WO2011049101A1 - Wire electro-discharge machining device - Google Patents

Abstract

Disclosed is a wire electro-discharge machining device which uses a wire electrode (8) to machine a workpiece (7) into a product, the workpiece (7) having varying thickness. The wire electrode (8) moves on a tool path (Q) where a product profile (P) is offset in an offset direction. The wire electro-discharge machining device comprises a step position estimation means (21) for performing an operation wherein a step position where the thickness of the workpiece (7) changes abruptly is estimated on the basis of three-dimensional shape data of the product, resulting in an estimated step position (Ps) being generated. Furthermore, the wire electro-discharge machining device comprises a step position detection means (37) for detecting the actual step position (Qs) of the workpiece (7) during machining of the workpiece (7), and a step position correction means (38) for correcting the estimated step position on the basis of the actual step position.

Description

Wire electrical discharge machine

The present invention relates to a wire electric discharge machining apparatus for machining a workpiece by generating an electric discharge in a machining gap formed between a wire electrode and a conductive workpiece. In particular, the present invention relates to a wire electric discharge machining apparatus for machining workpieces having different thicknesses into products.

Generally, a wire electric discharge machining apparatus has a wire electrode supported vertically between a pair of wire guides. During processing, the wire electrode is moved in the horizontal XY plane, and a dielectric liquid is injected into the processing gap. A typical dielectric liquid is water having a specific resistance of 5 × 10 4 to 1 × 10 5 Ω · cm. The wire electric discharge machining apparatus applies a voltage pulse to the machining gap in order to generate electric discharge. By applying voltage, the dielectric liquid is ionized, and electric discharge is generated in the machining gap.

As a result, current flows through the machining gap and the on-time starts. On-time is also called duration. When the on-time ends, the wire electric discharge machine stops supplying current and starts the off-time. The off time is also called a pause time. The wire electric discharge machining apparatus applies a voltage to the machining gap again when the off-time ends. In this way, current pulses are repeatedly supplied to the machining gap and the workpiece material is removed.

In order to balance the material removal rate, surface roughness and shape accuracy, the wire electrical discharge machining process is divided into several machining stages. Prior to the wire electrical discharge machining process, the tool path and machining conditions in the XY plane are determined for each machining stage. Initially, the wire electrode is moved over the first tool path, and the workpiece is roughly shaped by a large amount of energy. Such roughing is called “first cut”. When the first cut is completed, excess material remains on the cut surface, and the surface roughness of the cut surface does not meet the requirements.

Next, the cut surface is finished with high shape accuracy by small energy.仕 上 げ Such finishing includes several processing steps and is collectively referred to as “second cut”. During the second cut, the later the machining stage, the smaller the machining gap and the closer the tool path is to the product contour. Excess material is removed little by little to meet the requirements for shape accuracy and surface roughness.

Patent Documents 1 to 5 disclose wire electric discharge machining apparatuses that detect the thickness of a workpiece (hereinafter referred to as “plate thickness”) and change machining conditions in accordance with the plate thickness. The processing conditions are, for example, an on time, an off time, a peak of a current pulse, and an injection pressure of a dielectric liquid. In the wire electric discharge machining apparatus of these documents, the change of the machining conditions may be delayed at a position where the plate thickness changes rapidly (hereinafter referred to as “step position”).

Patent Document 6 discloses a wire electric discharge machining apparatus that calculates a plate thickness based on three-dimensional shape data of a workpiece and changes machining conditions according to the plate thickness. The three-dimensional shape data is created by a CAD device, for example. The step position estimated based on the three-dimensional shape data may be different from the actual step position.

Japanese Patent Publication No.59-332 Japanese Patent Publication No. 63-25889 Japanese Patent Publication No. 2-29453 Japanese Patent No. 3237895 Japanese Patent No. 3399736 JP 2007-290088 A

An object of this invention is to provide the wire electric discharge machining apparatus which can change a machining condition smoothly in the vicinity of a level | step difference position by specifying a level | step difference position more correctly.

A wire electric discharge machining apparatus for machining a workpiece (7) of varying thickness, in which a wire electrode (8) moves on a tool path (Q) in which a product contour (P) is offset in an offset direction, into a product,
Step position estimating means (21) for estimating a step position where the thickness of the workpiece changes rapidly based on the three-dimensional shape data of the product and generating an estimated step position (Ps);
A step position detecting means (37) for detecting an actual step position (Qs) of the workpiece during machining of the workpiece;
Step position correcting means (38) for correcting the estimated step position based on the actual step position is included.

The estimated step position (Ps) exists on the product contour (P), and the actual step position (Qs) may be on the tool path (Q). The step position correcting means (38) may correct the estimated step position (Ps) to a position where the actual step position (Qs) is moved in the direction opposite to the offset direction.

According to the present invention, the estimated step position is corrected based on the actual step position detected during the first cut. Therefore, in the second cut, the processing conditions can be changed based on a more accurate step position.

FIG. 1 is a front view showing a wire electric discharge machining apparatus of the present invention. FIG. 2 is a block diagram mainly showing the NC apparatus in FIG. FIG. 3 is a plan view showing an example of a workpiece. FIG. 4 is a side view showing an example of the workpiece of FIG. FIG. 5 is a flowchart showing the operation of the wire electric discharge machining apparatus.

The wire electric discharge machining apparatus of the present invention will be described with reference to the drawings. As shown in FIG. 1, a processing tank 5 is mounted on a bed. A table 6 is provided in the processing tank 5, and a workpiece 7 is fixed on the table 6. The processing tank 5 is filled with a dielectric liquid. The wire electrode 8 is vertically supported by upper and lower wire guides. The upper wire guide is housed in the upper nozzle assembly 3 and the lower wire guide is housed in the lower nozzle assembly 4. The upper and lower nozzle assemblies 3 and 4 are arranged so as to sandwich the workpiece 7. The upper and lower nozzle assemblies 3 and 4 are provided with nozzles that inject a dielectric liquid onto the wire electrode 8.

The wire electric discharge machining apparatus includes a CAD device 10, a CAM device 20, and an NC device 30. The wire electric discharge machining apparatus further includes a power supply device (not shown) that applies a voltage to a machining gap formed between the workpiece 7 and the wire electrode 8. The CAD device 10 is realized by executing the CAD program read into the auxiliary storage device of the general-purpose computer. By executing the CAD program, three-dimensional shape data of the product is obtained. The three-dimensional shape data is output to the CAM device 20 via the network 11.

As shown in FIG. 2, the CAM device 20 has a step position Ps at which the first plate thickness t1 on the product contour P rapidly changes to the second plate thickness t2 based on the three-dimensional shape data of the product. It functions as a step position estimating means 21 for estimating. As shown in FIG. 3, the step position Ps exists on the product contour P. The product contour P is also called a program trajectory. The step position estimating means 21 generates the estimated step position Ps in association with the plate thickness data. Further, the CAM device 20 functions as an NC program generating unit 22 that generates an NC program for executing wire electric discharge machining. The NC program includes an estimated step position Ps, a control start position P1, a control end position P2, plate thickness data t1, t2, an offset amount δ, and an offset direction.

As shown in FIG. 4, the workpiece 7 has a first plate thickness t1 at the control start position P1, and the workpiece 7 has a second plate thickness t2 at the control end position P2. The control start position P1 and the control end position P2 define a control range d. When the wire electrode 8 is positioned within the control range d, the first machining condition is smoothly changed to the second machining condition. The first processing condition is suitable for the first plate thickness t1, and the second processing condition is suitable for the second plate thickness t2. Since a sudden change in the processing conditions may cause the wire electrode 8 to break, the control range d is defined. A path Q (hereinafter, “tool path”) Q along which the wire electrode 8 moves in the XY plane during processing is shown in FIG. The tool path Q is a line in which the product contour P is offset by an offset amount δ in the offset direction. The offset direction is a normal direction to the product contour P.

As shown in FIG. 2, the NC device 30 includes an input device 31, a storage device 32, and a processing device 33, and has a function of performing wire electric discharge machining while correcting the estimated step position Ps on the product contour P. ing. The input device 31 includes, for example, a keyboard and a mouse. The operator can use the input device 31 to instruct the execution of the NC program.

The storage device 21 is composed of, for example, a hard disk and can store an NC program. The NC program is a program for machining the workpiece 7 by electric discharge machining. The NC program 22 includes a command for moving the wire electrode 8 and a command for supplying a dielectric liquid to the processing tank 5. The processing device 33 includes a CPU and a memory. The processing device 33 functions as an NC program reading unit 35, an electric discharge machining execution unit 332, a step position detecting unit 37, and a step position correcting unit 38, and plays a major role in correcting the estimated step position Ps in the NC program.

The NC program reading unit 35 has a function of reading the NC program from the storage device 32 in accordance with a command input by the operator using the input device 31. The electric discharge machining execution means 36 obtains the actual control start position Q1 on the tool path Q by moving the control start position P1 in the offset direction by the offset amount δ. Similarly, the actual control end position Q2 on the tool path Q is obtained based on the control end position P2. The electric discharge machining means 36 gradually switches from the first machining condition to the second machining condition while the wire electrode 8 moves from the position Q1 to Q2.

The step position detecting means 37 has a function of detecting the actual step position Qs for each processing stage. The actual step position Qs exists on the tool path Q. As shown in FIG. 2, the step position detecting means 37 is connected to the position detector 40, the discharge number detector 41 and the average gap voltage detector 42. The step position detecting means 37 can acquire the number of discharges and the average gap voltage every sampling time Δt only when the wire electrode 8 is within the control range d. The average gap voltage is an average of the machining gap voltages. The position detector 40 is provided for detecting the position of the wire electrode 8 on the tool path Q. The step position detecting means 37 calculates the thickness T of the workpiece 7 for each sampling time Δt according to Equation 1 based on the detected data.

Ｔ：工作物７の板厚（ｍｍ）
Ｈ：放電一発当たりの材料除去面積（ｍｍ^３）
ｎ：放電回数
Ｆ：ワイヤ電極８の送り速度（ｍｍ／分）
Ｖｇ：平均間隙電圧（Ｖ）
α，β，γ：演算係数

T: Thickness of workpiece 7 (mm)
H: Material removal area per discharge (mm ³ )
n: Number of discharges F: Feed rate of the wire electrode 8 (mm / min)
Vg: Average gap voltage (V)
α, β, γ: Calculation coefficients

The feed speed of the wire electrode 8 is calculated based on the position of the wire electrode 8 and the sampling time Δt. The calculation coefficient is determined by the material of the workpiece 7 and the wire electrode 8, for example. Further, the step position detecting means 37 detects the actual step position Qs on the tool path Q by comparing successive plate thicknesses T. Alternatively, the step position detecting means 37 may detect the step position Qs based on other values that vary in accordance with the change in the plate thickness, for example, the number of discharges, the average gap voltage, and the jet pressure of the dielectric liquid. The step position Qs is stored in the storage device 32 in association with the estimated step position Ps.

The step position correcting means 38 has a function of correcting the estimated step position Ps based on the actual step position Qs. The step position correcting means 38 obtains a step position PS on the product contour P. As shown in FIG. 3, the step position PS is a position PS where the actual step position Qs is shifted by an offset amount δ in the direction opposite to the offset direction. Then, the step position correcting means 38 replaces the estimated step position Ps with the step position PS before the start of the next processing stage. With the correction of the estimated step position Ps, the control start position P1 and the control end position P2 are also corrected.

The process in which the wire electric discharge machine corrects the estimated step position Ps will be described in detail with reference to the flowchart of FIG. First, the operator uses the CAD device 10 to generate three-dimensional shape data of a product. Based on the three-dimensional shape data of the product, the step position estimation means 21 of the CAM device 20 estimates the step position Ps in association with the plate thickness data t1 and t2.

In step S1, the NC program generating means 22 of the CAM device 20 includes the estimated step position Ps on the product contour P, the control start position P1, the control end position P2, the plate thickness data t1, t2, the offset amount δ, and the NC including the offset direction. Generate a program. The NC program is stored in the storage device 32 of the NC device 30.

The NC program reading means 35 reads the NC program from the storage device 32 in accordance with the operator input information. In step S2, the electric discharge machining execution means 36 starts the first cut according to the input information of the operator. In step S3, the position detector 40, the discharge number detector 41, and the average gap voltage detector 42 each start detecting data.

The step position detecting means 37 extracts the control start position P1 and the control end position P2 from the NC program. In step S <b> 4, the step position detection unit 37 compares the control start position P <b> 1 with the position of the wire electrode 8. When the wire electrode 8 reaches the control start position P1, the process proceeds to step S5, and the step position detecting means 37 starts to periodically calculate the plate thickness T.

The step position detecting means 37 obtains the number of discharges and the average gap voltage and calculates the feed speed. In step S5, the step position detecting means 37 calculates the plate thickness T every sampling time Δt. Further, the step position detecting means 37 calculates a difference between successive plate thicknesses T, that is, a change in plate thickness.

In step S6, the step position detecting means 37 compares the change in the plate thickness T with a predetermined value. If the change in the plate thickness T is greater than or equal to the predetermined value, the process proceeds to step S7. Otherwise, the process returns to S5. In step S7, the step position detecting means 37 detects the step position Qs where the plate thickness has changed abruptly. The actual step position Qs is stored in the storage device 32 in association with the estimated step position Ps in the NC program.

The step position correcting means 38 reads the actual step position Qs in the first cut from the storage device 32. The step position correcting means 38 obtains the step position PS by shifting the actual step position Qs by the offset amount δ in the direction opposite to the offset direction. In step S8, the step position correcting means 38 replaces the estimated step position Ps in the NC program with the step position PS before the start of the next machining stage. As a result, the control start position P1 and the control end position P2 on the NC program are also corrected.

If the electric discharge machining execution means 36 determines in step S9 that all estimated step positions Ps have been corrected, the process ends. Otherwise, the process returns to step S4. Although the process of correcting the estimated step position in the first cut has been described, a similar process may be executed in each processing stage of the second cut.

3 Upper nozzle assembly 4 Lower nozzle assembly 5 Processing tank 6 Table 7 Work piece 8 Wire electrode 10 CAD device 11 Network 20 CAM device 21 Step position estimating means 22 NC program generating means 30 NC device 31 Input device 32 Storage device 33 Processing Device 35 NC program reading means 36 Electric discharge machining execution means 37 Step position detecting means 38 Step position correcting means 40 Position detector 41 Number of discharges detector 42 Average gap voltage detector

Claims (3)

In a wire electric discharge machining apparatus for machining a workpiece (7) of varying thickness in which a wire electrode (8) moves on a tool path (Q) in which a product contour (P) is offset in an offset direction,
A step position estimating means for generating an estimated step position by estimating a step position where the thickness of the workpiece rapidly changes based on the three-dimensional shape data of the product;
A step position detecting means for detecting an actual step position of the workpiece during machining of the workpiece;
A wire electric discharge machining apparatus comprising step position correcting means for correcting the estimated step position based on the actual step position. The wire electric discharge machining apparatus according to claim 1, wherein the estimated step position exists on the product contour, and the actual step position exists on the tool path. The wire electric discharge machining apparatus according to claim 2, wherein the step position correcting means corrects the estimated step position to a position where the actual step position is moved in a direction opposite to the offset direction.

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